March 14, 2006

Research may help fish farmers manage diseases

by K.C. Jaehnig

CARBONDALE, Ill. -- Mother Nature knows best, at least where vitamin E. is concerned.

A researcher at Southern Illinois University Carbondale's Fisheries and Illinois Aquaculture Center has looked at how well the synthetic stuff performs compared to the kind extracted from plants when given to hybrid striped bass. She found it took less of the natural vitamin E to achieve the health effects provided by the standard, minimum daily requirement of the synthetic version.

"Natural source vitamin E is between 1.5 and 3 times more potent," said Jesse T. Trushenski, a doctoral student whose dissertation is focusing on her work with vitamin E. Her findings in effect establish the minimum amount of vitamin E from natural sources — 22 milligrams per kilogram of feed — that hybrid striped bass need in their diet to remain healthy.

"This had been established for other species, including humans, but not for fish," said Trushenski, one of only five graduate students selected two years ago from a nationwide pool for a fellowship from the National Sea Grant College Program,

The March issue of the quarterly North American Journal of Aquaculture includes a report of her results.

For Trushenski, however, these findings represent just a "jumping-off point," she said.

"It's useful to know, but more importantly it set the foundation for the rest of my research."

Trushenski hopes to use dietary changes to help fish farmers grow a more "robust" hybrid striped bass that can withstand both disease and stress. While results will prove particularly helpful to those who raise this high-value fish, her findings will have wider use.

"For aquaculture in general, disease is a problem," she noted.

"Farmers don't have a lot of contact with their livestock — basically, they see them only at feeding time. They know something's wrong if the fish go off their feed, but by then it's too late to do anything. Once you have a disease outbreak, there aren't a lot of treatment options.

"Stress is a problem with this particular species — more so than with catfish or salmon. They spook easily and when stressed come down with a number of diseases. Unfortunately, many necessary culture practices stress the fish, which means the stress is not temporary. It is a regular, if not constant, condition."

Trushenski thinks that giving the fish more natural vitamin E than they actually require might boost their immune systems, and at the cellular level she seems to be right. This phase of her research involved feeding the fish diets that included natural vitamin E doses ranging from twice to 100 times the minimum requirement for 12 weeks and then subjecting them to varying forms of stress.

"The stressors were easy to do but were also a good simulation of what would occur in a production facility in harvest and transport," she said.

"For mild stress, we would chase the fish with a net in the tank for one minute. For more severe stress, we would chase them, catch them and suspend them in a net crowded together for an hour."

Trushenski next analyzed blood and tissue samples to see how well the immune system killed bacteria and found that a dosage five times the minimum produced the best results.

She's now comparing the effect of both synthetic and natural vitamin E at the minimum and fivefold dosages on the health of fish exposed to actual diseases.

"We're hoping to see that the promising results we saw earlier actually translate into reduction in disease and infection rates," Trushenski said.

In addition, Trushenski is interested in the role vitamin E plays in how the body stores and burns fats, especially during exercise — a question that may have special interest for humans who aren't fish farmers. Fish on her vitamin E-enhanced diets are working out on a sort of fish treadmill, basically equipment that makes them swim against a current.

"Vitamin E seems to increase fat deposition in the abdominal area of fish, but it also increases the activity of enzymes which pull that fat out of the body and increase the ability of the body to use it," she said.

"We're seeing an increase in total availability of energy as we increase the vitamin E — it appears to increase the capacity for exhaustive exercise."

Leading in research, scholarly and creative activities is among the goals of Southern at 150: Building Excellence Through Commitment, the blueprint the University is following as it approaches its 150th anniversary in 2019.